Digital intensive techniques are useful to build wireless and wireline transmitters in deep-submicron processes. When high output powers with low noise are desired over a wide bandwidth signal, traditional linear in-phase (I)-quadrature (Q) modulator based techniques become challenging at low voltages. To produce a high amount of linear output power while operating at a low supply voltage is difficult for a class A or class AB amplifier. Furthermore, these amplifiers are not very efficient.
In contrast, digital power amplifiers (DPAs) use class-E type operation to produce output power. DPAs produce more or less output power by turning on more or fewer transistors. The number of transistors turned on or off determines the output signal magnitude as well as the output power. FIG. 1 shows a traditional IQ upconverter 5 comprising two mixers 10, 12 followed by an adder 14. The mixer 10 is driven by a local oscillator (LO) signal for the I modulated data, e.g., LOI, and the mixer 12 is driven by a LO signal for the Q modulated data, e.g., LOQ. The I/Q upconverter 5 is followed by a traditional power amplifier (PA) driver or a PA. The output signal is upconverted to radio frequency (RF) and fed to the class A or class AB PA driver (or a PA) that drives the output.
The upconversion principle can be mathematically described as rf(t)={I(t)+jQ(t)}ejωct that is, a frequency translation of the spectrum of the complex modulation signal I(t)+jQ(t) using a complex exponential waveform (cos ωct+j sin ωct), where ωc=2πfc. Digital signal processing techniques have allowed for development of more precise upconversion modulation schemes.